The dispersion polymerization of methyl methacrylate (MMA) has been studied in a nonpolar hydrocarbon solvent at low temperature using N, N-dimethylaniline (DMA) and lauroyl peroxide (LPO) as redox initiation system. To explain the heterogeneous kinetic characteristics of the polymerization process, the reaction locus has been experimentally and theoretically investigated. The evolutions of monomer conversion, polymer molecular weight distribution (MWD), and particle morphology were measured throughout the polymerization. It was found that the significant preferences of LPO and DMA to accumulate in the polymer-rich phase after the system phase separation are mainly responsible for both the uniformity of particle sizes and the broad polymer MWDs. It was observed that particle agglomeration and breakup mechanisms were enhanced under agitation, thus promoting the formation of broader particle size distributions. The observed kinetics and thermodynamics of the low-temperature polymerization were also examined through a mathematical model where the distributions of initiators, solvent, and monomer between phases were considered. A good agreement between the experimental and theoretical results was observed and the model was used to estimate the conditions that promote bimodal MWDs. POLYM. ENG. SCI., 51:1969-1986, 2011. (C) 2011 Society of Plastics Engineers